Fishtales - Spring 2006

The Nooksack Salmon Enhancement Association

Salmon of the Quarter: Sockeye and Kokanee
by Dave Beatty

Among the Pacific salmon, the sockeye (from the Indian name "sukkai", aka the red in Alaska), Oncorhynchus nerka, has the greatest diversity of life history patterns and is the third most abundant. Within the races of anadromous (sea-run) sockeye, there are lacustrine stocks and riverine stocks. Also, there are the lake and reservoir resident sockeye known as kokanee (aka the little redfish) and, occasionally, smaller descendants of sea-run sockeye, usually males, known as "residuals" that do not migrate to the ocean and remain as residents in freshwater. "Residualism" also occurs in coho and Chinook, but not in chum and pink salmon. Reproductive success of residuals is not well documented for any species. Kokanee (less than 1 kg) are smaller versions of anadromous sockeye (2-4 kg) and exhibit similar life cycle characteristics of sea-run sockeye except for the absence of the migratory behavior and the ocean phase.

Male sockeye, oncorhynchus nerka.

At sexual maturity, both forms exhibit an intense reddening of the body (especially in males) and males develop hooked jaws (kype) and a dorsal hump (less pronounced than in male pink salmon). Kokanee are polyphyletic; i.e., they originated independently many times from parental races of sea-run sockeye.

Consequently, the native kokanee in a lake are more closely related to the native sockeye (their ancestral stock) of that lake than they are to the native kokanee in another watershed. Lacustrine sockeye spawn in streams above or below lakes and after emergence from the gravel, the fry migrate downstream or upstream into the lake where they form schools (different from the territorial behavior of juvenile Chinook and coho while resident in freshwater). Lacustrine sockeye may also spawn along a lake shore providing there is suitable gravel and sufficient ground water upwelling through the gravel. Within a lake system, there may be stream and lake shore spawners. Juveniles of a lacustrine race remain in the lake for one or more years before smoltifying and migrating to the ocean.

Among the Pacific salmon, lacustrine sockeye stocks require the most precise homing mechanisms to complete the life cycle. Riverine sockeye spawn in streams and are not dependent on a lake for juvenile rearing. Instead, the juveniles may remain in the stream for a year or more ("river-type"); or they may outmigrate after a few months or shortly after emergence from the gravel ("sea-type"). The former juvenile behavior is similar to that of coho and "stream type" Chinook juveniles and that of the latter early outmigrants to "ocean type" Chinook juveniles and even to chum and pink juveniles. Similar to lacustrine sockeye, kokanee spawn in tributary streams or along the lake shore. When both sockeye and kokanee coexist, they do not interbreed.

Riverine kokanee are not known; likely because there were not the selective forces on riverine sockeye juveniles to remain in fresh water comparable to those on juveniles of a lacustrine race of sockeye. The age of Pacific salmon is given by a system involving the number of winters a juvenile spent in freshwater and, separated by a decimal point, the number of winters spent in the sea. A four year old spawning sockeye is designated 1.2, if it was a juvenile in freshwater for one winter followed by two winters in the ocean; however a four year old could be 0.3 (out migrated prior to a winter in fresh water). A spawning pink salmon is 0.1 (two years of age). Within a population of spawning sockeye, it is common to have a predominant age class. For example, the predominance of 1.2 adults (4 years of age) in the Fraser system and fewer 1.3 adults (5 years of age). This is exhibited in the well known Adams River sockeye run that peaks on a four year cycle. Among the five species of Pacific salmon throughout their natural ranges, sockeye have the largest number of age groups (14; however, the majority are in four age groups 1.2, 2.2, 1.3 and 2.3) and pinks have the least, only one age group (0.1).

In North America, the largest numbers of sockeye occur from the Columbia R. northward to the Kuskokwim River in Alaska. The major populations now center in the Fraser River and its numerous tributaries and lakes; in the Skeena River watershed on the northern British Columbia coast; and in the Copper River and Bristol Bay watersheds in Alaska, the latter producing over 50% of North American sockeye. The Columbia River ceased to be a major sockeye nursery when the Grand Coulee Dam was built in the 1930s. Prior to that, lakes in British Columbia were large producers of sockeye. Lake Wenatchee continues to generate sockeye.The near extirpation of sockeye from Redfish Lake in Idaho has coincided with the construction of the four lower dams on the Columbia River and the four dams on the Snake River. This "endangered" Snake River ESU is maintained by a captive brood stocking program with no natural spawning. On the Olympic Peninsula, the sockeye of Ozette Lake are listed as a "threatened" ESU.

Locally, lacustrine sockeye occur in Baker Lake. This stock is enhanced through the use of artificial spawning beds constructed and maintained in Baker Lake by Puget Sound Energy as part of the mitigation for the hydroelectric dams. Adults are trapped in the Baker River below Lake Shannon and trucked to Baker Lake.To reduce mortality in the turbines, smolts are trapped at the upper dam and transported to the lower Baker River for out migration to the ocean. Small numbers (a few hunded or less) of spawning riverine sockeye occur in the Nooksack and the Skagit Rivers. Each native population appears to be more closely related to northern riverine stocks than to local lacustrine stocks. Nooksack juveniles seem to exhibit both the "river-type" and the "sea-type" patterns for the length of freshwater residence. Lake Washington has a lacustrine stock (likely of Baker Lake origin) with spawning centered in the Cedar River that years ago was routed into Lake Washington. The enormous production of sockeye in the Fraser River system in comparison to the Columbia and Snake Rivers is a testament to the impact of dams in the latter two (there are no dams in the Fraser and Thompson River mainstems). However, the number of Fraser River sockeye and pink salmon began declining substantially after 1913 due to the dumping of rock and to a rock slide in 1914 at Hell's Gate (a natural constriction of the river in the Fraser Canyon) during railroad construction. These events caused a further constriction and a significantly increased vertical drop with much higher
water velocities at the time of upstream salmon migration. In the mid-1940s, fishways were built on both banks to facilitate fish passage past the constriction and the number of salmon produced upriver increased dramatically. In Asia, spawning sockeye occur from the Anadyr River in Russia southward along the coast to the southern tip of the Kamchatka Peninsula; along the northwest coast of the Sea of Okhotsk; and in the Kuril Islands. The major center of abundance is on the Kamchatka Peninsula. Again, both lacustrine and riverine stocks occur with riverine races often predominating due to scarcity of suitable lakes.

Kokanee have a natural distribution that coincides with that of lacustrine sockeye. Kokanee occur locally in Lake Whatcom where a state hatchery supplies eggs and juveniles for stocking lakes throughout the West and elsewhere; and in Lake Samish where there may have been a native stock but it has been commingled with the Lake Whatcom stock.

Sockeye do not occur in either lake; however, there is migratory connectivity between the ocean and Lake Samish. Kokanee have been successfully introduced into lakes throughout temperate regions of the world. Transplants of sockeye have had limited success and then only within the species natural range. This is also generally true for the other Pacific salmon species indicating that anadromy is difficult to establish.

After entering the ocean, sockeye undergo extensive migrations in the North Pacific Ocean comparable to those of chum and pink salmon and these three species often overlap with their Asian cousins. Chinook and coho tend to remain along the continental shelf, although some Chinook and coho do migrate farther into the open ocean. Sockeye feed on a diet rich in large zooplankton (crustaceans and fish larvae) which imparts the desirable red color and oil content to the most valuable species in the commercial salmon fishery.

For those readers desiring additional information on Pacific salmon, I can recommend the following books.

1) Behnke, R. J. 1992. Trout and salmon of North America. The Free Press, New York.

2) Groot, C. and L. Margolis, eds. 1991. Pacific salmon life histories. University of British Columbia Press, Vancouver.

3) Quinn, T. P. 2005. The behavior and ecology of Pacific salmon and trout. University of Washington Press.

4) Watson, R. 1999. Salmon, trout and charr of the world. Swan Hill Press, Shrewsbury, England.